Dynamic adsorption behaviors between Cu2+ ion and water-insoluble amphoteric starch in aqueous solutions

Dynamic adsorption behavior between Cu2+ ion and water-insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long-term stage. The diffusion rate of Cu2+ ion in both stages is concentration dependent. In the external mass-transport process, the diffusion coefficient (D-1) increases with increasing initial concentration in the low- (1 x 10(-3)-4 x 10(-3)M) and high-concentration regions (6 x 10(-3)-10 x 10(-3)M). The values of adsorption activation energy (K,,) in the low- and high-concentration regions are 15.46-24.67 and -1.80 to -11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D,) increases with increasing initial concentration in the low-concentration region (1 x 10(-3)-2 x 10(-3)M) and decreases with increasing initial concentration in the high-concentration region (4 x 10(-3)-10 x 10(-3)M). The k(d2) values in the low- and high-concentration regions are 9.96-15.30 and -15.53 to -10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low-concentration region and is exothermic in the high-concentration region for both stages. The external mass-transport process is more concentration dependent than the intraparticle diffusion process in the high-concentration region, and the dependence of concentration for both processes is about equal in the low-concentration region. (C) 2001 John Wiley & Sons, Inc.